Annunciator system



Filed .June 1, 1965 Sheet INVENTOR FOSTER EWELD I. Il oq @mjlwuq Ylvlllllll Feb. 25, 1969 y F. E. WELD 'ANNUNCIATOR SYSTEM Sheet FiledJune 1, 1965 United States Patent() 10 Claims ABSTRACT OF THE DISCLOSUREA solid state system for indicating that an alarm condition exists atany of a plurality of remote station monitoring circuits having a likeplurality of central station supervisory circuits, each electricallyvconnected with an associated one of the monitoring circuits, and acentral station common circuit which is connected to each of the centralstation supervisory circuits. An alarm signal indicative of an alarmcondition at the remote station is transmitted to the associatedsupervisory circuit which energizes an alarm indicator in the centralstation supervisory circuit and causes common alarm indicators in thecentral station common circuit to be energized. Each of the centralstation supervisory circuits also has a trouble indicator which isenergized by a disruption in the electrical connection between thesupervisory circuit and the associated monitoring circuit, and energizescommon trouble indicators in the central station common circuit. Aself-restoring reset switch common to both the common alarm indicatorsand the common trouble indicators at the central station common circuitdeenergizes the common alarm indicators and common trouble indicatorswhile the supervisory alarm indicator or supervisory trouble indicatorof any of the supervisory circuits remain energized, so that the centralstation common circuit may indicate an alarm or trouble -conditionassociated with another remote station monitoring circuit.

This invention is directed toward an annunciator system and, moreparticularly, to an improved annunciator system which providesindications in response to either an alarm condition at a monitoredstation or a trouble condition of the annunciator system itself.

Generally, annunciator systems are utilized to monitor the condition ofa device or environment at a remotely located station and provide visualand/or audible indications in accordance therewith at a centrallylocated star tion. An operator at the central station will take note ofthe visual and/ or audible indications to, for example, initiatecorrective measures.

A known annunciator system is described and illustrated in the patent toG. E. Foster 3,124,793 and includes generally a plurality of pairs ofnormally open contacts, each pair associated with one monitored deviceat a remotely located station; an equal plurality of supervisorycircuits, each including an alarm indicating lamp and circuitry forenergizing the lamp when an associated monitored 'device exhibits analarm condition; and, a common alert device and circuitry for energizingthe alert device when any monitored device exhibits an alarm condition.The above system does not provide indications so that the operator maydistinguish between an alarm condition at the monitored device and atrouble condition, such as an open circuit, of the system itself.

The present invention is directed toward an annunciator system whichprovides indications to an operator at a central station as to both analarm condition of a monitored device or environment and a troublecondition of the annunciator system itself, thereby overcoming the:1430331I Patented Feb. 25, 1969 noted disadvantages, and others, ofprevious annunciator systems.

In accordance with the present invention, the annunciator systemincludes a plurality of remote station monitoring circuits. eachincluding means to transmit an alarm signal `when an alarm condition hasoccurred at the remote station; a like plurality of central stationsupervisory circuits, each associated with one of the remote stationmonitoring circuits and including rst circuit means responsive to analarm signal for energizing supervisory alarm indicating means, andsecon-d circuit means responsive to a trouble condition of theassociated monitoring circuit for energizing supervisory troubleindicating means; and, a common central station circuit including commonalarm indicating means which 'becomes energized when the alarmindicating means of any supervisory circuit is energized, and a commontrouble indicating means which becomes energized when the troubleindicating means of any supervisory circuit is energized.

In accordance with a further aspect of the present invention, the commonalarm and trouble indicating means each include both visual and audibleindicating means.

In accordance with a further aspect of the present invention, eachsupervisory circuit and its associated monitoring circuit havesupervisory current of a given value normally flowing therethrough,which current is increased in value when the monitoring circuittransmits an alarm signal and the rst circuit means in the supervisorycircuit is responsive to the increased value of the supervisory currentto cause energization of the supervisory indicating means.

In accordance with a still further aspect of the present invention, thesecond circuit means in each supervisory circuit is responsive to adecrease or extinction in the value of the supervisory current to causeenergization of the supervisory trouble indicating means.

In accordance with a still further and preferred aspect of the presentinvention, each supervisory circuit and the common circuit includestatic element switching circuits.

The principal object of the present invention is to provide anannunciator system which has the capability of presenting indications toan operator of both alarm conditions at remote stations and troubleconditions of the annunciator system itself.

Another object of the present invention is to provide an annunciatorsystem having supervisory current ilowing therethrough, the increase invalue of which is representative of an alarm condition at a remotestation, and the Idecrease or loss in value of which is a troublecondition of the annunciator system itself.

A still further object of the present invention is to provide anannunciator system utilizing static switching circuits, such astransistors, whereby current requirements and, hence, power requirementsare maintained low for economically efficient operation.

The invention may take physical form in certain parts and arrangement ofparts, a preferred embodiment of which will be described in detail inthe specification and illustrated in the accompanying drawings which area part hereof, and wherein:

FIGURE l is a block diagram of the preferred embodiment of theinvention; and,

FIGURE 2 is a schematic circuit -diagram of the preferred embodiment ofthe invention.

Referring now to the drawings wherein the showings are for the purposeof illustrating a preferred embodiment of the invention only and not forthe purpose of limiting same, FIGURE 1 illustrates an annunciator systemincluding generally -a pair of remote station monitoring circuits A andB; and, central station equipment C including a pair of supervisorycircuits D and E, a power supply circuit F, and a common circuit G. The

monitoring circuits A and B may be located, as desired, at differentremote stations within the annunciator system. Each monitoring circuitserves the purpose of monitoring the condition of a device or anenvironment, such as temperature within a particular area and the like,to develop an alarm signal when a particular condition has occurred. Theoutput circuits of the monitoring circuits A and B are connected tosupervisory circuits D and E, located at the central station equipmentC. Supervisory circuit D includes an alarm lamp and a trouble lamp 12and, similarly, supervisory circuit E includes an alarm lamp 14 and Vatrouble lamp 16. The supervisory circuits D and E are connected to thecommon circuit G which has an alarm lamp 18, a trouble lamp 20, an alarmbell 22 and a trouble buzzer 24. The power supply circuit F serves toprovide power for operating supervisory circuits D and E, as well as thecommon circuit G.

The monitoring circuits A and B are substantially identical and thesupervisory circuits D and E `are substantially identical and,accordingly, the following description with reference to the schematiccircuit diagram, illustrated in FIGURE 2, is directed only towardmonitoring circuit A `and supervisory circuit D, along with the powersupply circuit F and the common circuit G.

Monitoring circuit The monitoring circuit A may take the form, asillustrated in FIGURE 2, of either a centralized monitoring circuit A ora decentralized monitoring circuit A. The monitoring circuits A' and Aare similar and each includes an end of line resistor 26 and a normallyopen switch 28 connected in parallel with resistor 26 across monitoringcircuit terminals X and Y. Switch 28 may be a manually operated switch,as shown, or any well known switching means, such as a bimetallicelement switch, so that in response to a particular condition the switchmay serve to short circuit the end of line resistor 26. The distinctionbetween the centralized monitoring circuit A and a decentralizedmonitoring circuit A" is that the latter circuit further includes itsown source of power taking the form, for example, ofbattery 30 havingits negative to positive sides connected in series from terminal X tothe parallel circuit of resistor 26 and switch 28. For purposes ofdiscussion, :monitoring circuit A is shown in FIGURE 2 with its outputterminals X and Y connected to the input circuit of supervisory circuitD through a current limiting resistor 32.

S upervsory circuit The input circuit of the supervisory circuit D istaken across a Zener diode 34, poled as shown in FIGURE 2, and which isin turn connected across terminals 2 and 5 of a double throw, doublepole switch S1 having a pair of movable contacts 36 and 38 connected toterminals 2 and 5, respectively. The movable contacts 36 and 38respectively serve to engage stationary contacts 1 and 4 when the inputcircuit of supervisory circuit D is connected across the decentralizedmonitoring circuit A or, as shown in FIGURE 2, to respectively engagestationary contacts 3 and 6 when the input circuit of supervisorycircuit D -is connected across the centralized monitoring circuit A. Ajumper wire, or conductor, 40 connects contacts 3 and 4 together.

Operating power for supervisory circuit D is obtained from the powersupply circuit F, which, for purposes of illustration, takes the form ofa battery 42 having its positive side connected to contact 6 of switchS1 and its negative side connected to contact 1 of switch S1. A voltagedivider taking the form of series connected resistors 44 and 46 isconnected between switch contact 3 and the negative side of battery 42,i.e., switch contact 1. A pair of series connected capacitors 48 and 49are connected in parallel with resistors 44 and 46, which in turn areconnected to a pair of NPN transistors 50 and 52. Transistor 50 has acollector 54 connected to the positive side of battery 42 through a pairof series connected resistors 56 and 58, a base 60 connected to one sideof resistor 44 at switch contact 3 and an emitter 62. Transistor 52includes an emitter 64 connected to the negative side of -battery 42, abase V66 connected to the junction of resistors 44 and 46 and acollector 68 connected to the emitter 62 of transistor 50 through thecathode to anode circuit of a diode 70.

The collector 68 of transistor 52 is connected to the base 72 of a NPNtransistor 74 which serves as an emitter follower circuit and includes acollector 76 connected to the positive side of battery 42 and an emitter78 connected to the negative side of battery 42 through a filament coil80 of supervisory trouble lamp 12. A load resistor 82 is connected inparallel with filament coil 80 and is connected from the negative sideof battery 42 to two supervisory output circuits, one including theanode to cathode circuit of a diode 84 and the other including acapacitor 86 connected in series with the anode to cathode circuit ofanother diode 88. The junction of capacitor 86 and the anode side ofdiode 88 is connected to the negative side of battery 42 through aresistor 90.

The junction of resistors 56 and 58 in the collector circuit oftransistor 50 is connected to the ibase 92 of a PNP transistor 94,having a collector 96 connected to the negative side of battery 42through a parallel circuit comprising a filament coil 98 of supervisoryalarm lamp 10 and a lo'ad resistor 100, and an emitter 102 connected tothe positive side of battery 42. A capacitor 104 is connected betweenthe base 92 and emitter 102 of transistor 94. Transistor 52 togetherwith diode 70 and a resistor 106, connected from the anode side of diode70 to the positive side of battery 42, serve as a reverse biasingcircuit for transistor 94. A pair of output circuits are taken from thejunction of load resistor and collector 96 of transistor 94, oneincluding the anode to cathode circuit of a diode 108 and the otherincluding a capacitor 110 in series with the anode to cathode circuit ofVa diode 112. The junction of capacitor 110 and the anode side of diode112 is connected to the negative side of battery 42 through a resistor114.

Common circuit 'Ilie common circuit G, schematically illustrated inFIGURE 2, includes a pair of series connected resistors 116 and 118,defining a voltage divider, connected across load resistor 100 in thecollector circuit of transistor 94, through capacitor .110 and the anodeto cathode circuit of diode 112. A capacitor is connected in parallelacross resistors 116 and 118 and the junction of the resistors isconnected to the gate 122 of a silicon controlled rectilier 124.Rectifier 124 'has an anode ,126 connected to the junction of collector96 of transistor 94 and load resistor 100 through the anode to cathodecircuit of diode i108 and a resistor 128. Rectifier 124 also has acathode connected to the negative side of battery 42 through a resistor132 and a normally closed, manually operable switch S2. The junction ofresistor 132 and the cathode 130 of rectifier 124 is connected to thebase 134 of a NPN transistor 136, having an emitter 138` connected tothe negative side of battery 42 through switch S2 and a collector 140connected to the positive side of battery 42 through a pair of seriesconnected resistors 142 and 144. The junction of resistors 142 and 144is connected to the base 146 of a NPN transistor 148, having an emitter150 connected to the positive side of battery 42 through the anode tocathode circuit of a diode 152. The transistor 148 also includes acollector 154 connected to the negative side of battery 42 through aparallel circuit including the common alarm bell 22 and a filament coil156 of alarm lamp 18.

The common circuit G also includes a pair of series connected resistors158 and 160, defining a voltage divider, connected across load resistor82 in the emitter circuit of transistor 74 through capacitor 86 and theanode to cathode circuit of diode 88. A capacitor 162 is connected inparallel across resistors 158 and 160 and vthe junction of the resistorsis connected to the gate 164 of a silicon controlled rectifier 166. Therectier 166 has an anode 168 connected to the junction of load resistor82 and emitter 78 of transistor 74, through the anode to cathode circuitof diode 84 and a resistor 170, and a cathode 172 connected to thenegative side of battery 42 through a resistor 174 and switch S2. Thejunction of resistor 174 and cathode 172 of rectifier 166 is connectedto the base 176 of a NPN transistor 180, having an emitter 182 connectedto the negative side of battery 42 through switch S2 and a collector 184connected to the positive side of battery 42 through a pair of seriesconnected resistors 186 and 188. The junction of resistors 186 and 188is connected to the base 190 of a PNP transistor 192 having an emitter194 connected to the positive side of battery 42 through the anode tocathode circuit of a diode 196. Transistor 192 also has a collector 198connected to the negative side of battery 42 through a parallel circuitincluding a diode 200 connected in series with trouble buzzer 24, and afilament coil 202 of trouble lamp 20.

Operation During the operation of the annunciator system, as illustratedin FIGURE 2, supervisory current normally ows from the positive side ofbattery 42 through a current path including switch contacts 6 and 38,the end of line resistor 26, resistor 32, resistor 44 and resistor 46 tothe negative side of battery 42. Preferably, the supervisory current isof a given value, such as 1 milliampere direct current, and is ofsufficient value that a positive potential will be present on base 66 oftransistor 52 with respect to emitter 64, whereby transistor 52 will beforward biased and conductive. With transistor 52 conductive, currentwill also ow from the positive side of battery 42 through resistor 106,the anode to cathode circuit of diode 70, and from the collector toemitter of transistor 52 to the negative side of battery 42. The forwardresistance of diode 70, however, is suciently large iwith respect to theseries resistance of resistors 44 and 46 that the potential appearing onthe emitter 62 will be more positive than that appearing on the base 60of transistor 50, iwhereby transistor 50 will be maintained reversedbiased and nonconductive. So long as the supervisory current ismaintained at substantially the given value, i.e., at l milliampere,transistor 50 will be maintained reversed biased and nonconductive andtransistor 52 will be maintained forward biased and conductive and boththe alarm lamp 10 and trouble lamp 12 of the supervisory circuit D willremain de-energized. Also, so long as alarm lamp 10 is maintainedde-energized the common circuit lamp 18, as well as the common circuitalarm bell 22, will not become energized, and that so long assupervisory circuit trouble lamp 12 is maintained de-energized thecommon circuit trouble lamp 20 and the common circuit trouble buzzer 24will not become energized. This is the normal operating condition of theannunciator system.

In a manner similar to that as described above, a normal operatingcondition of the annunciator system may be obtained by substituting thedecentralized monitoring circuit A" for the centralized monitoringcircuit A', shown connected to the input circuit of supervisory circuitD in FIGURE 2. When monitoring circuit A" is connected to the input`circuit of supervisory circuit D, and with switch S1 in itsdecentralized position, i.e., with movable ycontact 36 in engagementwith switch contact 1 and movable contact 38 in engagement with switchcontact 4, supervisory current of the given value, preferably on theorder of l milliampere, will normally flow from the positive side ofbattery 30 through the end of line resistor 26, switch contacts 38, 4and 3, resistors 44 and 46, and through switch contacts 1 and 36 to thenegative side of battery 30 through resistor 32. As described withrespect to the centralized monitoring circuit A', the supervisorycurrent is of suicient magnitude that transistor 52 will be forwardbiased and conductive, and current twill ow from the positive side ofbattery 42 through diode 70 and the collector to emitter of transistor52 to the negative side of battery 42, `whereby transistor 50 willbecome reversed biased and nonconductive. Other than the foregoingmanner in which supervisory current is obtained, the operation of theannunciator system is the same Whether the centralized monitoringcircuit A or the decentralized monitoring circuit A is connected to theinput circuit of supervisory `circuit D.

The description of operation of the annunciator system illustrated inFIGURE 2 is hereinafter continued with reference to the centralizedmon'itoring circuit A' being connected, as shown, to input circuit ofsupervisory circuit D. When the switch 28 is monitoring circuit A'becomes closed in response to a predetermined condition of a monitoreddevice or environment, such as temperature, the end of line resistor 2-6will be short circuited whereby the supervisory current will beincreased in value from, for example, 1 milliampere to 3 milliamperes,so that the potential across resistors 44 and 46 will surticientlyincrease in value that the potential 'appear-ing on base 60 oftransistor 50 will become positive with respect to that appearing onemitter 62. Thus, the transistor 50 will become forward biased andconductive. When transistor 50 is conduct-ive, current will flow fromthe positive side of battery 42 through resistors 58, 56, the collectorto emitter circuit of transistor 50, the anode to cathode circuit ofdiode 70, and from the collector to emitter circuit of transistor 52 tothe negative side of battery 42. Thus, a voltage will appear acrossresistor 58, whereby the potential appearing on base 92 of transistor 94will become less positive with respect to that appearing on emitter 102.Thus, transistor 94 will become forward biased and conductive, andcurrent will flow from the positive side of battery 42 through theemitter to collector crcuit of transistor 94 and thence through theparallel path including load resistor and filament 98 of lamp 10,whereby lamp 10 will glow brightly indicative of an alarm condition atmonitoring circuit A.

When current flows through load resistor 100, a positive potential willappear across resistor 100, which potential will be applied to the anode126 of silicon controlled rectifier 124 in the common circuit G throughthe anode to cathode circuit of diode 108 and resistor 128. Capacitor110 in supervisory circuit D Will be charged by current ow therethroughfrom the positive side of battery 42 Ithrough the emitter to collectorcircuit of transistor 94, the capacitor 110, the anode to cathodecircuit of diode 112, and the series connected res-istors 116 and 118 tothe negative side of battery 42 through switch S2. The capacitorcharging current will exist for a period in accordance with the RC timeconstant as determined by the values of capacitor 110, the forwardresistance of diode 112 and the resistors 116 and 118. When thiscapacitor charging current is flowing a voltage pulse will be developedacross resistor 118 in the common circuit G, which pulse will be ofpositive polarity and of suicient magnitude that the voltage exist-ingon gate 122 of silicon controlled rectier 124 will be positive withrespect to that appearing on cathode 130, whereby the rectier 124 willbecome forward biased and conductive. Thus, current will flow from thepositive side of battery 42 through t-he emitter to collector circuit oftransistor 94, through the anode to cathode circuit of diode 108, theresistor 128, the anode to cathode circuit of rectier 124, and thencethrough resistor 132 through switch S2 to the negative side of battery42. A voltage will be developed across resistor 132 so that a positivevoltage will appear on base 13'4 of transistor 136 with respect to thaton emitter 138, whereby transistor 136 will become forward biased andconductive. Current will then ow from the positive side of battery 4'2through resistors 144 and 142, the collector to emitter circuit oftransistor 136 to the negative side of battery 4'2 through the switchS2. A voltage will be developed across resistor 144 so that the voltage-on emitter 150 on transistor 148 will be positive with respect to thaton base 146, whereby the trausistor 148 will become forward biased andconductive. Thus, current will flow from the positive side of battery42, through the anode to cathode circuit of diode 152, the emitter tocollector circuit of transistor 148, energizing both the common circuitalarm bell 22 and the -filament 156 of the common circuit alarm lamp 18.The operator after noting the alarm ind-ications may press switch S2 to`momentarily provide an open circuit to the negative side of battery 42,de-energizing silicon controlled rectifier 12'4. Thus, transistors 1-36and 150 will become de-energized, caus-ing bell 2'2 and lamp 18 tobecome de-energized. The momentary opening of switch S2, however, willnot result in de-energization of alarm lamp in the supervisory circuit Dsince with switch 28 closed the increased value of supervisory currentflowing through resistors 44 Iand 46 will continue to maintaintransistor 94 forward biased and conductive. Lamp 10 Will remainenergized until corrective action is taken trated in FIGURE 2, it ispossible that the supervisory current will decrease in value to lessthan that of the given value, i.e., 1 milliampere, or even beextinguished, such as upon an open circuit in the interconnectionbetween monitoring' circuit A or A" and supervisory circuit D, or uponloss rof power resulting from failure of battery 30 if the decentralizedmonitoring circuit A" is connected to the `supervisory circuit D, etc.When the supervisory current has decreased in Value below `1 milliamperetransistor 52 will become reverse bia-sed and nonconductive so that thevoltage appearing on base 7-2 of transistor 74 will be positive withrespect to that on emitter 78. Thus, transistor 74 will become forwardbiased and current will flow from the positive Vside of battery 42through the collector to emitter circuit of transistor 74 and thencethrough filament y80 of lamp 1-2 and through the load resistor 82. Thetrouble `lamp 12 will, therefore, become energized providing a visualindication of a trouble condition. The contage developed across resistor82, due to current flow therethrough, will be coupled to the anode ofsilicon controlled rectifier 166 through the anode to cathode circuit ofdiode 84 and resistor 170 ls0 that the voltage appearing on anode 168 ispositive with respect to that on cathode 172. Capacitor y86 will becomecharged by current llowing therethrough from the positive side ofbattery 42 through the collector to emitter circuit of transistor 7-4,the capacitor 86, the anode to cathode circuit of diode '88, the seriesconnected resistors 158 and 1-60 of common circuit G and, thence,through switch S2 to the negative side of battery 42. The chargingcurrent will exist for a period in accordance with the RC time constant,determined by the values of capacitor 86, the forward resistance ofdiode 88 and re- -sistors 158 and 1,60. During the period that capacitorcharging current is lilowing, a voltage pulse will be developed acrossresistor 160 -so that, yin turn, `a positive voltage pulse will appearon gate 164 of silicon controlled rectifier 166 with respect to cathode172 so that the rectifier becomes forward biased and conductive. Thus,current will flow from the positive side of battery 42 through thecollector to emitter circuit of transistor 74, the anode to cathodecircuit of diode 84, resistor 170, the `anode to cathode circuit ofrectifier 166, the resistor 174 and thence through the switch S2 to thenegative side of battery I42. A voltage will be developed acrossresistor 174 so that a positive voltage will be applied to the base 176of transistor 180 with respect to emitter A182, whereby transistor 180becomes forward biased and conductive. Current will ilow from thepositive side of battery 42 through resistors 1'88, 186, the collectorto emitter circuit of transistor 1'80, and thence to the negative sideof battery 42 through the switch S2. A voltage will be developed acrossresistor 188 lso that the voltage appearing on emitter 194 of transistor192 will 'be positive with respect to that on base 190, wherebytransistor 192 will become forward biased and conductive. Accordingly,current will flow from the positive side of battery 42 through the anodeto cathode circuit of diode 196, the emitter to collector circuit oftransistor 192, the anode to cathode circuit of diode 200, the troublebuzzer 24, and also through the parallel circuit including the filament202 of trouble lamp 20 and to the negative side of battery `42. Thecommon circuit trouble buzzer '24, as well as the common circuit troublelamp 20, will become energized presenting an operator with both audibleand visual trouble indications. The operator, after noting the troubleindications by buzzer 24 and lamp 20 at the common circuit G, maymomentarily depress switch S2 thereby placing an open circuit in thecathode circuit of silicon controlled rectifier 166 to the negative sideof battery 42. Thus, rectier 166 will cease to conduct, de-energizingtransistors 180 and 1192, lamp 20 and bell 24. The trouble lamp 12 inthe supervisory circuit D will, however, be maintained energized untilthe supervisory current is restored to its normal value at which timetransistor 52 will become forward biased and conductive, thereby causingtransistor 74 to become nonconductive, de-energizing lamp 12.

In accordance with a preferred embodiment of the invention, the valuesand types of various components illustrated in FIGURE 2 are found `inTable I.

TableI Component: Component value or type Battery -30 volts-- 2() End ofline resistor 26 kilohms 11 Zener diode 34 IN3031 Resistor 32 ohms 600Capacitor 48 microfarad 0.05 Capacitor 49 do 2.0 yResi-Stor 44 ohms 200Resistor 46 do 600 Resistor 58 do -270 Resistor 56 kilohms 1.8Transistor 50 2NI302 Transistor 52 -2'NI302 Diode 70 -E'D3002 Capacitor104 microfarads 2.0 Resistor 106 kilohms 1.8 Transistor 94 2NI415vResistor kilohms 5.1 Resistor i82 do 5.1 Transistor 74 2N'I302Capacitor microfarads 2.0 Capacitor 86 do 2.0 Resistor 90 kilohms `100Resistor 114 do 100 Diode v84 ED3002 Diode 88 ED3002 Diode 108 EDSOOQDiode 112 ED3002 lResistor 116 kilohm-- 1 Resistor 118 ohms 160Capacitor 120 microfarad-- 0.05 Silicon controlled re'ctier 124 2N2323Resistor 128 ki1ohm 1 Resistor 13'2 ohms 270 Transistor 136 -2NI302Resistor 142 kilohms I=1 Resistor 14'4 ohms 270 IDiode 152 microfaradsED3002 Transistor 148 2NI501 Resistor 1'58 kilohm-- 1 lResistor ohms 150'Capacitor 162 microfarad 0.05 Silicon .controlled rectifier 166 l2N23239 Table I-Contz'nued Component: Component value or type Resistor 170kilohm Resistor 188 ohms-- 270 Resistor 186 kilohm 1 Transistor 180y2NI302 Resistor 186 kilohm-- l Resistor 18S ohms-.. 270 Diode 196microfarads-- EDSOOZ Transistor 192 2NI501 Although the invention hasbeen shown in connection with a preferred embodiment, it will be readilyapparent to those skilled in the art that various changes in form andarrangement of parts may be made to suit requirements without departingfrom the spirit and scope of the invention.

I claim:

1. An annunciator system comprising:

a plurality of remote station monitoring circuits, each of saidmonitoring circuits having means for transmitting an alarm signalindicative of an alarm condition at the remote station;

a like plurality of central station supervisory circuits eachelectrically connected with an associated one of said monitoringcircuits, means for indicating an alarm in each said supervisorycircuit, first circuit means for energizing said alarm indicating meanslin response to said alarm signal, means for indicating trouble in eachsaid supervisory circuit, second circuit means for energizing saidtrou'ble indicating means in response to a disruption in said electricalconnection between said supervisory circuit and said associatedmonitoring circuit;

a central station common circuit having common alarm indicating meansand common trouble indicating means and third and fourth circuit meansfor respectively energizing said common alarm and common troubleindicating means when said supervisory alarm and supervisory troubleindicating means of any of said supervisory circuits become energized;and,

said central station common circuit also having means for respectivelydeenergizing said common alarm and common trouble indicating means whilesaid supervisory alarm or said supervisory trouble indicating means ofany of said supervisory circuits remain energized.

2. An annunciator system as set foith in claim 1, wherein saiddeenergizing means is common to said third and fourth circuit energizingmeans.

3. An annunciator system as set forth in claim 2, Wherein saiddeenergizing means is a normally closed self-restoring switch.

4. An annunciator system as set forth in claim 1, wherein saidsupervisory circuit and its associated monitoring circuit forms asupervisory current circuit, and a source of voltage is connected withinsaid current circuit so that supervisory current of a given valuenormally ows in said current circuit.

5. An annunciator system as set forth in claim 4, wherein said voltagesource is located at said associated monitoring circuit.

6. An annunciator system as set forth in claim 4, wherein saidassociated monitoring circuit includes means for increasing the value ofsaid supervisory current consist ing of said alarm signal.

7. An annunciator system as set forth in claim 6, Wherein saidsupervisory current circuit includes a resistor so that the voltagedeveloped across said resistor will be increased in value when the valueof said supervisory current is increased; and,

said iirst circuit means includes a normally nonconductive electroniccontrol means having an input circuit connected to said resistor and anoutput circuit coupled to said supervisory alarm indicating means, saidcontrol means being conductive when the voltage across said resistorattains a predetermined Value whereby current will ow through saidcontrol means to energize said supervisory alarm indicating means.

8. An annunicator system as set forth in claim 4, Wherein saidsupervisory current circuit includes a resistor so that the voltagedeveloped across said resistor will be decreased in value when the valueof said supervisory current is decreased; and,

said second circuit means includes a normally conductive electroniccontrol means having an input circuit connected to said resistor and anoutput circuit coupled to said supervisory trouble indicating means,said normally conductive control means being nonconductive when thevoltage across said resistor is decreased in value from said givenvalue, said supervisory trouble indicating means being energized whensaid normally conductive control means becomes nonconductive.

9. An annunciator system as set forth in claim 1, Wherein said commoncircuit includes a resistor having current flow therethrough when saidsupervisory alarm indicating means is energized; and,

said third circuit means includes an electronic control means having aninput circuit connected to said resistor and an output circuit coupledto said common alarm indicating means, said control means beingconductive when current ows through said resistor and said common alarmindicating means being energized when said control means becomesconductive.

10. An annunciator system as set forth in claim 1, wherein said commoncircuit includes a resistor having current oW therethrough when saidsupervisory trouble indicating means is energized; and,

said fourth circuit -means includes an electronic control means havingan input circuit connected to said resistor and an output circuitcoupled to said common trouble indicating means, said control meansbeing conductive when current ows through said resistor and said commontrouble indicating means being energized when said control means becomesconductive.

References Cited UNITED STATES PATENTS 2,116,947 5/1938 Ketay 340-4092,895,125 7/ 1959 Watts 340-409 2,944,251 7/ 1960 Tetherow 340-409THOMAS B. HABECKER, Primary Examiner.

U.S. Cl. X.R. 340--326

